The field of the invention relates to control systems for controlling engine air/fuel operation in response to exhaust gas sensors.
U.S. Pat. No. 4,132,200 discloses a feedback control system in which a feedback signal is generated by comparing an exhaust gas oxygen sensor output to a reference signal. The reference signal is generated by time averaging the sensor output. During open loop control, fuel is delivered in relation to a fuel signal which is biased rich and dithered. When an average in the number of sensor output transitions beyond the reference value exceeds a threshold, feedback control is initiated.
The inventors herein have recognized numerous problems with the above approaches. For example, the switch from open loop to feedback control may be delayed beyond the time at which the exhaust gas oxygen sensor is sufficiently heated to fully operable. This delay occurs because two averages are needed requiring numerous cycles of the sensor output. One average is required to generate the reference signal, and another average of the comparison between sensor output and the reference is also required. The need remains to more quickly and accurately determine when the sensor becomes fully operable and feedback control is commenced.